Solid state imagers generate electrical signals in response to light reflected by an object being imaged. Complementary metal oxide semiconductor (CMOS) imaging sensors are one of several different known types of semiconductor-based imagers, which include for example, charge coupled devices (CCDs), photodiode arrays, charge injection devices and hybrid focal plane arrays.
Some inherent limitations in CCD technology have promoted an increasing interest in CMOS imagers for possible use as low cost imaging devices. A fully compatible CMOS sensor technology enabling a higher level of integration of an image array with associated processing circuits would be beneficial to many digital image capture applications. CMOS imagers have a number of desirable features, including for example low voltage operation and low power consumption. CMOS imagers are also compatible with integrated on-chip electronics (control logic and timing, image processing, and signal conditioning such as A/D conversion). CMOS imagers allow random access to the image data, and have lower manufacturing costs, as compared with conventional CCDs, since standard CMOS processing techniques can be used to fabricate CMOS imagers. Additionally, CMOS imagers have low power consumption because only one row of pixels needs to be active at any time during readout and there is no charge transfer (and associated switching) from pixel to pixel during image acquisition. On-chip integration of electronics is particularly desirable because of the potential to perform many signal conditioning functions in the digital domain (versus analog signal processing) as well as to achieve reductions in system size and cost.
Nevertheless, demands for enhanced resolution of CCD, CMOS and other solid state imaging devices, and a higher level of integration of image arrays with associated processing circuitry, are accompanied by a need to improve the light sensing characteristics of the pixels of the imaging arrays. For example, it would be beneficial to minimize if not eliminate the loss of light transmitted to individual pixels during image acquisition and the amount of crosstalk between pixels caused by light being scattered or shifted from one pixel to a neighboring pixel.
Accordingly, there is a need and desire for an improved solid state imaging device, capable of receiving and propagating light with minimal loss of light transmission to a photosensor. There is also a need and desire for improved fabrication methods for imaging devices that provide a high level of light transmission to the photosensor and reduce the light scattering drawbacks of the prior art, such as crosstalk.